Responses of Hyalella azteca and Ceriodaphnia dubia to reservoir sediments following chelated copper herbicide applications

In response to nuisance growths of algae and vascular plants, such as dioecious hydrilla (Hydrilla verticillata L.f. Royle), copper formulations have been applied in lakes and reservoirs for a number of years. Concerns have arisen regarding the long-term consequences of copper applications and those concerns have appropriately focused on sediment residues. In this study, we evaluated the toxicity of sediments from treated (for a decade) and untreated areas in Lake Murray, South Carolina and estimated the capacity of those sediments to bind additional copper. Two sentinel aquatic invertebrates, Hyalella azteca Saussure and Ceriodaphnia dubia Richard, were used to measure residual toxicity of treated and untreated sediments from the field and after laboratory amendments. The copper concentrations in sediments were not significantly different for the treated and the untreated areas in Lake Murray and no toxicity was observed with either experimental organism or for sediments from either site. Based on the copper binding capacity of the collected Lake Murray sediments, the sediment copper concentration would have to increase eleven fold (from 16.3 to 180 mg Cu/ kg) before adverse effects are observed if no new binding sites accrue. Measures of sediment copper concentrations coupled with toxicity testing using sensitive sentinel invertebrates provide evidence of a lack of bioavailable copper due to excess sediment binding capacity for copper at these sites.